Help me with number 6 please its esay

Hurry which of these is true about index fossils? a) are very scarcely found b) used as guides in relative dating c) found in the youngest layer of the rock d) used as reference points in absolute dating

How do you date a sample of rock that you suspect as being one of the earliest on earth

Q: a: in sexually reproducing animals, once fertilization of the egg takes place, the exists as a single cell until cell division begins